Airbags and airbag systems are known in the art and are now standard on motor vehicles. These airbag systems generally are designed such that in the event of an accident or a crash, an inflatable airbag will become positioned between a vehicle occupant and an interior object or surface and will prevent the vehicle occupant from harmful impact with a portion of the vehicle interior. As is known in the art, airbags are currently added to the vehicle's steering wheel, dashboard, and/or at other locations within the vehicle. The inclusion of these airbag systems within motor vehicles have been credited with saving many lives and preventing many injuries.
Many typical airbag systems comprise several individual components joined to form an operational module. Such components generally include an airbag cushion, an airbag inflator, a sensor, and an electronic control unit. Airbag cushions are typically made of a thin, durable fabric that is folded to fit into a compartment of a steering wheel, dashboard, interior compartment, roof, roof rail, seat, or other space in a vehicle. The airbag inflator is designed to produce a gas to rapidly inflate the cushion when needed. The sensors detect sudden decelerations of the vehicle that are characteristic of an impact. The readings taken by the sensors are processed in the electronic control unit using an algorithm to determine whether a collision has occurred.
Upon detection of an impact of sufficient severity, the control unit sends an electrical signal to the inflator. The inflator uses one of many technologies, including pyrotechnic compounds and/or pressurized gas, to produce a volume of inflation gas. The inflation gas is channeled into the airbag, rapidly inflating it. Inflation of the airbag causes it to deploy, placing it in position to receive the impact of a vehicle occupant. After contact of the occupant with the airbag and the corresponding deceleration of the occupant, the airbag deflates, freeing the occupant to exit the vehicle.
Airbag apparatuses have been primarily designed for deployment in front of an occupant between the upper torso and head of an occupant and the windshield or instrument panel. However, alternative types of airbags such as knee bolsters and overhead airbags operate to protect various parts of the body from collision. Side impact airbags such as inflatable curtains and seat mounted airbags also have been developed in response to the need for protection from impacts in a lateral direction, or against the side of the vehicle.
It has been discovered that various parts of the body require different levels of impact protection. For example, a seat mounted airbag may inflate beside an occupant in a vehicle seat to protect the pelvis and thorax of the occupant against lateral impact. The weight of the occupant may generally tend to slide with the pelvis; hence, it may be beneficial for the pelvis portion of the seat mounted airbag to inflate stiffly to provide comparatively firm protection. By contrast, the thorax is more sensitive and generally carries less mass, and thus should preferably be more softly cushioned during impact to avoid potential injury to an occupant's ribs.
Dual chambered side impact airbags have been developed to provide a pressure differential between the pelvis and thorax portions of a side airbag. These airbags have two separate chambers, typically one on top of the other. The top chamber is used for providing impact protection for the thorax of an occupant in a seat and the bottom chamber is used to provide impact protection for an occupant's pelvis. In these systems, an inflator is placed in a housing that has multiple orifices for channeling inflation gases into both chambers. The pelvis chamber is inflated to a higher pressure than that of the thorax chamber.
Often a single inflator is used to deliver inflation gas to both the top chamber and the lower chamber. The single stream of inflation gas is channeled into both chambers by way of a diffuser. By varying the cross sectional areas of ports providing fluid communication between the diffuser and the chambers, the relative pressure of each of the chambers can be controlled. However, as the required pressure differential grows, there exists the potential for backflow wherein the inflation gas contained in the high-pressure chamber flows back into the low-pressure chamber by way of the fluid communication provided within the diffuser. As a result, it is difficult to obtain the high pressures required for the pelvis portion of the airbag while simultaneous inflating the thorax portion of the airbag to a low pressure.
Accordingly, there is a need in the art for a type of air bag that allows a single inflator to inflate multiple chambers within an airbag to pressure differentials greater than that currently available.